Scarlet fever probably didn't blind Mary Ingalls from "Little House on the Prairie"

New research looked into the real reason Laura Ingalls Wilder's sister Mary went blind.

Publicity photograph dated 1974 of actress Melissa Sue Anderson playing Mary Ingalls of the television series Little House on the Prairie. New medical research is shedding light on why the real Mary Ingalls went blind. (NBC Television/Wikimedia commons)

Fans of children's literature know how the story goes. Mary Ingalls from the "Little House on the Prairie" series got a bad case of scarlet fever and went blind.

But new medical research shows that the real life older sister of Laura Ingalls Wilder may have suffered from a brain infection instead, reports CNN.

The real Mary Ingalls did go blind when she was 14, in 1879. In her novel "By the Shores of Silver Lake" author Laura Ingalls Wilder described how scarlet fever had taken over the Ingalls household.

"Mary and Carrie and baby Grace and Ma had all had scarlet fever. The Nelsons across the creek had had it too, so there had been no one to help Pa and Laura. The doctor had come every day; Pa did not know how he could pay the bill. Far worst of all, the fever had settled in Mary’s eyes, and Mary was blind."

Dr. Beth Tarini, one of the co-authors of new study published in the journal Pediatrics, has been curious about Mary's blindness since she was a medical student, reports CBS.

"Since I was in medical school, I had wondered about whether scarlet fever could cause blindness because I always remembered Mary's blindness from reading the Little House stories and knew that scarlet fever was once a deadly disease," Tarini said in a press release.

"I would ask other doctors, but no one could give me a definitive answer, so I started researching it."

Tarini and a team of researchers spent more than a decade pouring over old papers and letters written by Laura Ingalls Wilder and matching them with mentions in the local newspaper and data on blindness and infectious diseases of the 1800s.

The team decided that the more logical explanation for Mary's blindness was not scarlet fever, but viral meningoencephalitis. That likely caused optic neuritis, or inflammation of her optic nerves, which resulted in her vision loss, reports NBC.

In a 1937 letter to her daughter, Rose, Ingalls Wilder wrote, "Mary had spinal meningitis [sic] some sort of spinal sickness. I am not sure if the Dr. named it. We learned later when Pa took her from De Smet, South Dakota to Chicago, Illinois to a specialist that the nerves of her eyes were paralyzed and there was no hope."

According to NBC, the register for Mary's school, the Iowa College for the Blind, lists her cause of blindness as "brain fever."

So why spend a decade researching a long ago case of blindness? Tarini told the New York Times that poor Mary from "Little House on the Prairie" is the first thing they think of when they hear their kids might have scarlet fever.

"In my mind, it’s no different than a strep throat with a rash, but the specter of history colors their reaction," she said.

“We’re taught to find out what’s wrong and give a patient a diagnosis,” Dr. Tarini continued, “but that’s only one of the things the patient needs. If I say ‘scarlet fever’ and a mother is thinking, ‘Mary Ingalls’ then if I don’t know to pull that out, I’m not doing my job.”